Raise clear error for multiple variadic arguments

[Fridayai700]

Summary

Closes #260.

When a command has more than one argument annotated with List[...] (or any type that maps to nargs=-1), Click raises an opaque TypeError: Cannot have two nargs < 0. This PR adds early validation in Typer's parameter collection to detect multiple variadic arguments and raise a clear UsageError explaining the constraint.

Changes

• Added validation after parameter collection in get_params_convertors_ctx_param_name_from_function() to check for multiple arguments with nargs < 0
• Raises click.UsageError with a message naming all conflicting arguments
• Added test test_multiple_list_arguments_error in tests/test_type_conversion.py

Example

Before:

TypeError: Cannot have two nargs < 0

After:

UsageError: Only one argument can take multiple values (nargs=-1), but 2 were found: 'names', 'others'. Use List[...] (or Sequence[...]) for at most one argument.